1. Field of the Invention
The present invention relates to a downhole steam apparatus for generating steam in situ to facilitate oil recovery from relatively deep wells.
2. Description of the Prior Art
Initial production from an oil well utilizes the pressure of gases in the oil formation. This is followed by pumping when the gas pressure diminishes. Eventually, even pumping is inadequate to produce acceptable quantities of oil and resort must be had to secondary recovery methods. These include thermal stimulation of the well by raising the temperature of the oil formation to lower the oil viscosity and enhance its flow.
Various types of thermal stimulation have been utilized, including electric or hot water heaters, gas burners, in-situ combustion, and hot water or steam injection. Of these, steam injection has many advantages.
Present systems for injecting steam are not effective in deep wells. In most such systems the steam is generated on the surface and piped down through the casing to the base of the borehole. In a deep well a considerable amount of heat is lost through the casing, and the temperature and quality of the steam is generally inadequate to effectively thermally stimulate formations at the base of the borehole.
Prior art attempts to generate steam in-situ or downhole have been ineffective since combustion requires that the fuel and air be provided at the pressure of the steam discharged from the combustor. The size and complexity of air compressors required to provide such high pressure become economically prohibitive.
An effective system of generating steam of high quality and temperature in-situ is desirable because flooding the formation with such steam has been found to significantly lower the flow resistance of the oil in the vicinity of the borehole, thereby enabling extraction of the displaced oil. The steam penetrates and heats the formation over a considerable distance, and consequently oil production is greatly improved in viscous oil-bearing sands from which pumping is impractical.